As is generally well known in the railway industry, truck mounted braking systems comprise a series of force transmitting members, levers and linkages which function to move a group of brake shoes against the wheels of a railway vehicle to effect stoppage of such railway vehicle. A pneumatically activated brake cylinder is typically provided in the braking system to initiate movement of this series of force transmitting members, levers and linkages to apply the brakes of the railway vehicle. A well known type of truck mounted braking system is a TMX.RTM. truck mounted braking system (TMX.RTM. is a registered trademark of Westinghouse Airbrake company, the assignee of the present invention).
A currently used pneumatically activated brake cylinder for TMX.RTM. truck mounted braking systems is shown in FIG. 2 and comprises an air cylinder piston which moves in a forwardly direction within a cylindrical member upon the application of pneumatic pressure thereto. A sealing means is provided on, or adjacent, a first end of the piston. This sealing means contacts the inner surface of the cylindrical member so as to provide an airtight chamber at one end of the cylindrical member such that application of pneumatic pressure therein and against the first end of the piston enables forward movement of the piston. A piston rod is attached at a second end of the piston and moves in accordance with movement of the piston. An opposite end of the piston rod is connected to the end of a push rod which is, in turn, connected to a cylinder force transfer lever. This cylinder force transfer lever is connected through a series of force transmitting members and linkages so as to initiate a braking sequence and consequently apply the brake shoes to the vehicle wheels.
A disadvantage of this type of pneumatically activated brake cylinder is that, due to regulations regarding the amount of air pressure which must be supplied into the brake cylinder, it is sometimes difficult to control the movement and/or force applied by the piston. During light load conditions, too much force applied by the piston can cause the brake shoe forces to be greater than necessary resulting in wheel skid.